This invention relates to a programmable controller, and particularly to a programmable controller which can monitor a suitable instruction execution stage.
As is known, programmable controller, can be provided with a trace function which monitors the instruction execution stage in order to debug the user program or determine the operating state of a controlled system.
However, the trace function provided on the conventional programmable controller is designed so that when specific address information is received, the execution content of an instruction corresponding to said address can be monitored. That is, the conventional trace function is such that controlling is effective in relatively simple cases, so that if one instruction is read, the execution of this instruction is determined to be a particular part of a control flow. For example, this is the case where the instruction execution is successively carried out from the leading address of the user program memory.
For this reason, where control becomes complicated and instructions which vary the control flow (such as jump instructions) are included in the program, the conventional trace function fails to determine if the read instruction is present in a particular route of the control flow.